Irrigation systems that deliver water, often containing plant nutrients, pesticides and/or medications, to plants via networks of irrigation pipes are very well known. In many such irrigation networks, water from the pipes is delivered to the plants by “emitters” or “drippers”, hereinafter generically referred to as emitters, that are installed on or “integrated” inside the irrigation pipes Emitters that are integrated inside an irrigation pipe are conventionally referred to as “integrated” emitters. Generally, the integrated emitters in a given irrigation pipe are equidistant from each other and each provides a substantially same flow rate of water for a same given water pressure in the pipe. However, integrated emitters in an irrigation pipe are not necessarily the same and equidistant from each other. Distances between emitters and emitter characteristics installed in a pipe may be adapted at the factory to particular requirements of a location at which the pipe is to be used and the conditions under which the pipe is to be used at the location.
For example, U.S. Pat. No. 6,308,902, the disclosure of which is incorporated herein by reference, describes a drip irrigation hose for irrigating plants comprising a plurality of integrated emitters having different discharge rates that are “manufactured into the hose”. The emitters have at least two different geometries that provide different resistances to water flow. Locations of the emitters along the pipe are determined so that emitters that are characterized by larger resistance to water flow are located at positions along the pipe that are subject to higher water pressure and emitters characterized by lower resistance to water flow are located at positions subject to lower water pressure. For example, assume that an irrigation pipe is to be used to irrigate plants in a relatively flat field. Higher resistance emitters are positioned along the pipe relatively close to an input end of the pipe, which is connected to a water source that provides water to the pipe and where water pressure is relatively high and close to the water inlet pressures Lower resistance emitters are positioned at locations relatively far from the water source at locations where water pressure is reduced relative to the inlet pressure because of resistance of the pipe to water flow. By positioning the emitters in this manner, flow rate of water provided by the pipe to irrigate the plants tends to be relatively uniform along the pipe length.
U.S. Pat. No. 4,423,838, the disclosure of which is incorporated herein by reference, describes “a custom designed topographically matched irrigation line” comprising “a multiplicity of liquid discharge means” that has desired water output characteristics along the length of the line. “The desired output characteristics are provided by “varying the periodicity of the discharge elements therealong varying the flow rates of the individual discharge elements or both in any desired combination.”
Whereas irrigation pipes configured to specific terrains and conditions for which they are to be used are beneficial, irrigation requirements, even over a same terrain, generally change over time, as, for example, crops in a field or terraced garden mature and/or their density in the field or garden changes A given configuration of emitters, even when tailored to meet the needs of a particular terrain and irrigation application can often not meet needs or the terrain and application as the needs change over a growing season. Typically, to meet changing needs during a growing season, a user of irrigation pipes will procure pipes having a density of emitters per unit length of pipe that is too high for an initial irrigation application for which the pipe is used. Some of the emitters are removed from operation by blocking, e g. by taping, their outputs to adapt the pipe to initial use Subsequently, in the event that the pipe is required to provide increased quantities of water, the blocked emitters are unblocked. Alternatively, a pipe may be procured with a quantity of emitters sufficient for an initial use requiring a relatively small provision of water. As demand for water increases, additional emitters are added, for example by coupling on-line emitters (emitters coupled externally to an irrigation pipe via holes that are often formed in the pipe wall using special tools) or self-puncturing emitters to the irrigation pipe. By way of example, self puncturing emitters are described in PCT Application PCT/IL2005/001382 entitled “Fluid Flow Control Regulator”, the disclosure of which is incorporated herein by reference.
U.S. Pat. No. 6,027,048, the disclosure of which is incorporated herein by reference, describes an integrated irrigation emitter suitable for integration in an irrigation pipe that has a non-return feature that seals the emitter against backflow of water and air into the pipe when pressure of water in the pipe falls below a predetermined level. The non-return feature reduces the frequency with which the emitters become clogged with dirt and debris carried by water and/or air backflow. Water and/or air backflow typically occurs when supply of water to irrigation pipes providing water to plants in a field or hothouse is turned off and pressure in the pipes falls. For subsurface drip irrigation (SDI) pipes, which are buried in the ground or a growing medium, particulate matter in the surrounding soil or growing medium tends to be drawn into and clog emitters in the pipes when water pressure in the pipes falls For above surface drip irrigation, backflow tends to clog emitters by drawing into the emitters particulate matter in mud and dust in environments in which the emitters often are located.
U.S. Pat. No. 5,615,838, the disclosure of which is incorporated herein by reference, describes integrated emitters, referred to as in-line emitters, that have a non-return feature and optionally provides a regulated flow of water. In an embodiment of the invention a flexible membrane closes the emitter to flow into or out of the emitter when inlet pressure to the emitter falls below a minimum pressure. The membrane optionally functions to control a length of a labyrinth through which water flows responsive to inlet pressure to regulate flow of water provided by the emitter. The patent notes that the “structures defining how and under what pressures the valves operate also can be readily varied”.
Whereas non-return irrigation emitters reduce probability of clogging as a result of their advantageous anti-clogging characteristic, when water supply to an irrigation pipe in which they are installed is turned off, they seal the pipe against ingress of air and prevent water in the pipe from draining out. As a result, storing the pipe after use or moving the pipe from one venue to another can require a relatively tedious draining process If water is drained from a far end of the pipe, for example from an end far from a water source to which the pipe is coupled, as the water drains, vacuum is created in the pipe that causes the pipe to collapse and fold in on itself. When the pipe collapses, not only is there a tendency for the pipe walls and emitters in the pipe to sustain damage but the collapse is not uniform, causing substantial variation in the shape and diameter of the pipe along its length. If the pipe is rolled up onto a spool, as is often the case after use during a growing season or in order to move the pipe from one field to another, “winding” of the pipe onto the spool is not uniform and tends to be tangled. Subsequently, when the irrigation pipe is unrolled from the spool, the non-uniform winding and tangles tend to make it difficult to unroll and lay the pipe evenly on the ground and/or tend to cause the pipe to “catch” and get caught on the spool during unrolling. If the pipe is unrolled by tractor, the jumbled winding and tangles generally make the task tedious and time consuming and if the pipe catches, can result in the pipe tearing or being otherwise damaged